nand_util.c: Correct licensing

[u-boot] / drivers / mtd / nand / docg4.c

/*
 * drivers/mtd/nand/docg4.c
 *
 * Copyright (C) 2013 Mike Dunn <mikedunn@newsguy.com>
 *
 * SPDX-License-Identifier:     GPL-2.0+
 *
 * mtd nand driver for M-Systems DiskOnChip G4
 *
 * Tested on the Palm Treo 680.  The G4 is also present on Toshiba Portege, Asus
 * P526, some HTC smartphones (Wizard, Prophet, ...), O2 XDA Zinc, maybe others.
 * Should work on these as well.  Let me know!
 *
 * TODO:
 *
 *  Mechanism for management of password-protected areas
 *
 *  Hamming ecc when reading oob only
 *
 *  According to the M-Sys documentation, this device is also available in a
 *  "dual-die" configuration having a 256MB capacity, but no mechanism for
 *  detecting this variant is documented.  Currently this driver assumes 128MB
 *  capacity.
 *
 *  Support for multiple cascaded devices ("floors").  Not sure which gadgets
 *  contain multiple G4s in a cascaded configuration, if any.
 */


#include <common.h>
#include <asm/arch/hardware.h>
#include <asm/io.h>
#include <asm/bitops.h>
#include <asm/errno.h>
#include <malloc.h>
#include <nand.h>
#include <linux/bch.h>
#include <linux/bitrev.h>
#include <linux/mtd/docg4.h>

/*
 * The device has a nop register which M-Sys claims is for the purpose of
 * inserting precise delays.  But beware; at least some operations fail if the
 * nop writes are replaced with a generic delay!
 */
static inline void write_nop(void __iomem *docptr)
{
        writew(0, docptr + DOC_NOP);
}


static int poll_status(void __iomem *docptr)
{
        /*
         * Busy-wait for the FLASHREADY bit to be set in the FLASHCONTROL
         * register.  Operations known to take a long time (e.g., block erase)
         * should sleep for a while before calling this.
         */

        uint8_t flash_status;

        /* hardware quirk requires reading twice initially */
        flash_status = readb(docptr + DOC_FLASHCONTROL);

        do {
                flash_status = readb(docptr + DOC_FLASHCONTROL);
        } while (!(flash_status & DOC_CTRL_FLASHREADY));

        return 0;
}

static void write_addr(void __iomem *docptr, uint32_t docg4_addr)
{
        /* write the four address bytes packed in docg4_addr to the device */

        writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
        docg4_addr >>= 8;
        writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
        docg4_addr >>= 8;
        writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
        docg4_addr >>= 8;
        writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
}

/*
 * This is a module parameter in the linux kernel version of this driver.  It is
 * hard-coded to 'off' for u-boot.  This driver uses oob to mark bad blocks.
 * This can be problematic when dealing with data not intended for the mtd/nand
 * subsystem.  For example, on boards that boot from the docg4 and use the IPL
 * to load an spl + u-boot image, the blocks containing the image will be
 * reported as "bad" because the oob of the first page of each block contains a
 * magic number that the IPL looks for, which causes the badblock scan to
 * erroneously add them to the bad block table.  To erase such a block, use
 * u-boot's 'nand scrub'.  scrub is safe for the docg4.  The device does have a
 * factory bad block table, but it is read-only, and is used in conjunction with
 * oob bad block markers that are written by mtd/nand when a block is deemed to
 * be bad.  To read data from "bad" blocks, use 'read.raw'.  Unfortunately,
 * read.raw does not use ecc, which would still work fine on such misidentified
 * bad blocks.  TODO: u-boot nand utilities need the ability to ignore bad
 * blocks.
 */
static const int ignore_badblocks; /* remains false */

struct docg4_priv {
        int status;
        struct {
                unsigned int command;
                int column;
                int page;
        } last_command;
        uint8_t oob_buf[16];
        uint8_t ecc_buf[7];
        int oob_page;
        struct bch_control *bch;
};
/*
 * Oob bytes 0 - 6 are available to the user.
 * Byte 7 is hamming ecc for first 7 bytes.  Bytes 8 - 14 are hw-generated ecc.
 * Byte 15 (the last) is used by the driver as a "page written" flag.
 */
static struct nand_ecclayout docg4_oobinfo = {
        .eccbytes = 9,
        .eccpos = {7, 8, 9, 10, 11, 12, 13, 14, 15},
        .oobavail = 7,
        .oobfree = { {0, 7} }
};

static void reset(void __iomem *docptr)
{
        /* full device reset */

        writew(DOC_ASICMODE_RESET | DOC_ASICMODE_MDWREN, docptr + DOC_ASICMODE);
        writew(~(DOC_ASICMODE_RESET | DOC_ASICMODE_MDWREN),
               docptr + DOC_ASICMODECONFIRM);
        write_nop(docptr);

        writew(DOC_ASICMODE_NORMAL | DOC_ASICMODE_MDWREN,
               docptr + DOC_ASICMODE);
        writew(~(DOC_ASICMODE_NORMAL | DOC_ASICMODE_MDWREN),
               docptr + DOC_ASICMODECONFIRM);

        writew(DOC_ECCCONF1_ECC_ENABLE, docptr + DOC_ECCCONF1);

        poll_status(docptr);
}

static void docg4_select_chip(struct mtd_info *mtd, int chip)
{
        /*
         * Select among multiple cascaded chips ("floors").  Multiple floors are
         * not yet supported, so the only valid non-negative value is 0.
         */
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;

        if (chip < 0)
                return;         /* deselected */

        if (chip > 0)
                printf("multiple floors currently unsupported\n");

        writew(0, docptr + DOC_DEVICESELECT);
}

static void read_hw_ecc(void __iomem *docptr, uint8_t *ecc_buf)
{
        /* read the 7 hw-generated ecc bytes */

        int i;
        for (i = 0; i < 7; i++) { /* hw quirk; read twice */
                ecc_buf[i] = readb(docptr + DOC_BCH_SYNDROM(i));
                ecc_buf[i] = readb(docptr + DOC_BCH_SYNDROM(i));
        }
}

static int correct_data(struct mtd_info *mtd, uint8_t *buf, int page)
{
        /*
         * Called after a page read when hardware reports bitflips.
         * Up to four bitflips can be corrected.
         */

        struct nand_chip *nand = mtd->priv;
        struct docg4_priv *doc = nand->priv;
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;
        int i, numerrs;
        unsigned int errpos[4];
        const uint8_t blank_read_hwecc[8] = {
                0xcf, 0x72, 0xfc, 0x1b, 0xa9, 0xc7, 0xb9, 0 };

        read_hw_ecc(docptr, doc->ecc_buf); /* read 7 hw-generated ecc bytes */

        /* check if read error is due to a blank page */
        if (!memcmp(doc->ecc_buf, blank_read_hwecc, 7))
                return 0;       /* yes */

        /* skip additional check of "written flag" if ignore_badblocks */
        if (!ignore_badblocks) {
                /*
                 * If the hw ecc bytes are not those of a blank page, there's
                 * still a chance that the page is blank, but was read with
                 * errors.  Check the "written flag" in last oob byte, which
                 * is set to zero when a page is written.  If more than half
                 * the bits are set, assume a blank page.  Unfortunately, the
                 * bit flips(s) are not reported in stats.
                 */

                if (doc->oob_buf[15]) {
                        int bit, numsetbits = 0;
                        unsigned long written_flag = doc->oob_buf[15];

                        for (bit = 0; bit < 8; bit++) {
                                if (written_flag & 0x01)
                                        numsetbits++;
                                written_flag >>= 1;
                        }
                        if (numsetbits > 4) { /* assume blank */
                                printf("errors in blank page at offset %08x\n",
                                       page * DOCG4_PAGE_SIZE);
                                return 0;
                        }
                }
        }

        /*
         * The hardware ecc unit produces oob_ecc ^ calc_ecc.  The kernel's bch
         * algorithm is used to decode this.  However the hw operates on page
         * data in a bit order that is the reverse of that of the bch alg,
         * requiring that the bits be reversed on the result.  Thanks to Ivan
         * Djelic for his analysis!
         */
        for (i = 0; i < 7; i++)
                doc->ecc_buf[i] = bitrev8(doc->ecc_buf[i]);

        numerrs = decode_bch(doc->bch, NULL, DOCG4_USERDATA_LEN, NULL,
                             doc->ecc_buf, NULL, errpos);

        if (numerrs == -EBADMSG) {
                printf("uncorrectable errors at offset %08x\n",
                       page * DOCG4_PAGE_SIZE);
                return -EBADMSG;
        }

        BUG_ON(numerrs < 0);    /* -EINVAL, or anything other than -EBADMSG */

        /* undo last step in BCH alg (modulo mirroring not needed) */
        for (i = 0; i < numerrs; i++)
                errpos[i] = (errpos[i] & ~7)|(7-(errpos[i] & 7));

        /* fix the errors */
        for (i = 0; i < numerrs; i++) {
                /* ignore if error within oob ecc bytes */
                if (errpos[i] > DOCG4_USERDATA_LEN * 8)
                        continue;

                /* if error within oob area preceeding ecc bytes... */
                if (errpos[i] > DOCG4_PAGE_SIZE * 8)
                        __change_bit(errpos[i] - DOCG4_PAGE_SIZE * 8,
                                     (unsigned long *)doc->oob_buf);

                else    /* error in page data */
                        __change_bit(errpos[i], (unsigned long *)buf);
        }

        printf("%d error(s) corrected at offset %08x\n",
               numerrs, page * DOCG4_PAGE_SIZE);

        return numerrs;
}

static int read_progstatus(struct docg4_priv *doc, void __iomem *docptr)
{
        /*
         * This apparently checks the status of programming.  Done after an
         * erasure, and after page data is written.  On error, the status is
         * saved, to be later retrieved by the nand infrastructure code.
         */

        /* status is read from the I/O reg */
        uint16_t status1 = readw(docptr + DOC_IOSPACE_DATA);
        uint16_t status2 = readw(docptr + DOC_IOSPACE_DATA);
        uint16_t status3 = readw(docptr + DOCG4_MYSTERY_REG);

        MTDDEBUG(MTD_DEBUG_LEVEL3, "docg4: %s: %02x %02x %02x\n",
            __func__, status1, status2, status3);

        if (status1 != DOCG4_PROGSTATUS_GOOD ||
            status2 != DOCG4_PROGSTATUS_GOOD_2 ||
            status3 != DOCG4_PROGSTATUS_GOOD_2) {
                doc->status = NAND_STATUS_FAIL;
                printf("read_progstatus failed: %02x, %02x, %02x\n",
                       status1, status2, status3);
                return -EIO;
        }
        return 0;
}

static int pageprog(struct mtd_info *mtd)
{
        /*
         * Final step in writing a page.  Writes the contents of its
         * internal buffer out to the flash array, or some such.
         */

        struct nand_chip *nand = mtd->priv;
        struct docg4_priv *doc = nand->priv;
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;
        int retval = 0;

        MTDDEBUG(MTD_DEBUG_LEVEL3, "docg4: %s\n", __func__);

        writew(DOCG4_SEQ_PAGEPROG, docptr + DOC_FLASHSEQUENCE);
        writew(DOC_CMD_PROG_CYCLE2, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);
        write_nop(docptr);

        /* Just busy-wait; usleep_range() slows things down noticeably. */
        poll_status(docptr);

        writew(DOCG4_SEQ_FLUSH, docptr + DOC_FLASHSEQUENCE);
        writew(DOCG4_CMD_FLUSH, docptr + DOC_FLASHCOMMAND);
        writew(DOC_ECCCONF0_READ_MODE | 4, docptr + DOC_ECCCONF0);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);

        retval = read_progstatus(doc, docptr);
        writew(0, docptr + DOC_DATAEND);
        write_nop(docptr);
        poll_status(docptr);
        write_nop(docptr);

        return retval;
}

static void sequence_reset(void __iomem *docptr)
{
        /* common starting sequence for all operations */

        writew(DOC_CTRL_UNKNOWN | DOC_CTRL_CE, docptr + DOC_FLASHCONTROL);
        writew(DOC_SEQ_RESET, docptr + DOC_FLASHSEQUENCE);
        writew(DOC_CMD_RESET, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);
        write_nop(docptr);
        poll_status(docptr);
        write_nop(docptr);
}

static void read_page_prologue(void __iomem *docptr, uint32_t docg4_addr)
{
        /* first step in reading a page */

        sequence_reset(docptr);

        writew(DOCG4_SEQ_PAGE_READ, docptr + DOC_FLASHSEQUENCE);
        writew(DOCG4_CMD_PAGE_READ, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);

        write_addr(docptr, docg4_addr);

        write_nop(docptr);
        writew(DOCG4_CMD_READ2, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);
        write_nop(docptr);

        poll_status(docptr);
}

static void write_page_prologue(void __iomem *docptr, uint32_t docg4_addr)
{
        /* first step in writing a page */

        sequence_reset(docptr);
        writew(DOCG4_SEQ_PAGEWRITE, docptr + DOC_FLASHSEQUENCE);
        writew(DOCG4_CMD_PAGEWRITE, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);
        write_addr(docptr, docg4_addr);
        write_nop(docptr);
        write_nop(docptr);
        poll_status(docptr);
}

static uint32_t mtd_to_docg4_address(int page, int column)
{
        /*
         * Convert mtd address to format used by the device, 32 bit packed.
         *
         * Some notes on G4 addressing... The M-Sys documentation on this device
         * claims that pages are 2K in length, and indeed, the format of the
         * address used by the device reflects that.  But within each page are
         * four 512 byte "sub-pages", each with its own oob data that is
         * read/written immediately after the 512 bytes of page data.  This oob
         * data contains the ecc bytes for the preceeding 512 bytes.
         *
         * Rather than tell the mtd nand infrastructure that page size is 2k,
         * with four sub-pages each, we engage in a little subterfuge and tell
         * the infrastructure code that pages are 512 bytes in size.  This is
         * done because during the course of reverse-engineering the device, I
         * never observed an instance where an entire 2K "page" was read or
         * written as a unit.  Each "sub-page" is always addressed individually,
         * its data read/written, and ecc handled before the next "sub-page" is
         * addressed.
         *
         * This requires us to convert addresses passed by the mtd nand
         * infrastructure code to those used by the device.
         *
         * The address that is written to the device consists of four bytes: the
         * first two are the 2k page number, and the second is the index into
         * the page.  The index is in terms of 16-bit half-words and includes
         * the preceeding oob data, so e.g., the index into the second
         * "sub-page" is 0x108, and the full device address of the start of mtd
         * page 0x201 is 0x00800108.
         */
        int g4_page = page / 4;                       /* device's 2K page */
        int g4_index = (page % 4) * 0x108 + column/2; /* offset into page */
        return (g4_page << 16) | g4_index;            /* pack */
}

static void docg4_command(struct mtd_info *mtd, unsigned command, int column,
                          int page_addr)
{
        /* handle standard nand commands */

        struct nand_chip *nand = mtd->priv;
        struct docg4_priv *doc = nand->priv;
        uint32_t g4_addr = mtd_to_docg4_address(page_addr, column);

        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s %x, page_addr=%x, column=%x\n",
            __func__, command, page_addr, column);

        /*
         * Save the command and its arguments.  This enables emulation of
         * standard flash devices, and also some optimizations.
         */
        doc->last_command.command = command;
        doc->last_command.column = column;
        doc->last_command.page = page_addr;

        switch (command) {
        case NAND_CMD_RESET:
                reset(CONFIG_SYS_NAND_BASE);
                break;

        case NAND_CMD_READ0:
                read_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
                break;

        case NAND_CMD_STATUS:
                /* next call to read_byte() will expect a status */
                break;

        case NAND_CMD_SEQIN:
                write_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);

                /* hack for deferred write of oob bytes */
                if (doc->oob_page == page_addr)
                        memcpy(nand->oob_poi, doc->oob_buf, 16);
                break;

        case NAND_CMD_PAGEPROG:
                pageprog(mtd);
                break;

        /* we don't expect these, based on review of nand_base.c */
        case NAND_CMD_READOOB:
        case NAND_CMD_READID:
        case NAND_CMD_ERASE1:
        case NAND_CMD_ERASE2:
                printf("docg4_command: unexpected nand command 0x%x\n",
                       command);
                break;
        }
}

static void docg4_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
{
        int i;
        struct nand_chip *nand = mtd->priv;
        uint16_t *p = (uint16_t *)buf;
        len >>= 1;

        for (i = 0; i < len; i++)
                p[i] = readw(nand->IO_ADDR_R);
}

static int docg4_read_oob(struct mtd_info *mtd, struct nand_chip *nand,
                          int page)
{
        struct docg4_priv *doc = nand->priv;
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;
        uint16_t status;

        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: page %x\n", __func__, page);

        /*
         * Oob bytes are read as part of a normal page read.  If the previous
         * nand command was a read of the page whose oob is now being read, just
         * copy the oob bytes that we saved in a local buffer and avoid a
         * separate oob read.
         */
        if (doc->last_command.command == NAND_CMD_READ0 &&
            doc->last_command.page == page) {
                memcpy(nand->oob_poi, doc->oob_buf, 16);
                return 0;
        }

        /*
         * Separate read of oob data only.
         */
        docg4_command(mtd, NAND_CMD_READ0, nand->ecc.size, page);

        writew(DOC_ECCCONF0_READ_MODE | DOCG4_OOB_SIZE, docptr + DOC_ECCCONF0);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);

        /* the 1st byte from the I/O reg is a status; the rest is oob data */
        status = readw(docptr + DOC_IOSPACE_DATA);
        if (status & DOCG4_READ_ERROR) {
                printf("docg4_read_oob failed: status = 0x%02x\n", status);
                return -EIO;
        }

        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: status = 0x%x\n", __func__, status);

        docg4_read_buf(mtd, nand->oob_poi, 16);

        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        writew(0, docptr + DOC_DATAEND);
        write_nop(docptr);

        return 0;
}

static int docg4_write_oob(struct mtd_info *mtd, struct nand_chip *nand,
                           int page)
{
        /*
         * Writing oob-only is not really supported, because MLC nand must write
         * oob bytes at the same time as page data.  Nonetheless, we save the
         * oob buffer contents here, and then write it along with the page data
         * if the same page is subsequently written.  This allows user space
         * utilities that write the oob data prior to the page data to work
         * (e.g., nandwrite).  The disdvantage is that, if the intention was to
         * write oob only, the operation is quietly ignored.  Also, oob can get
         * corrupted if two concurrent processes are running nandwrite.
         */

        /* note that bytes 7..14 are hw generated hamming/ecc and overwritten */
        struct docg4_priv *doc = nand->priv;
        doc->oob_page = page;
        memcpy(doc->oob_buf, nand->oob_poi, 16);
        return 0;
}

static int docg4_block_neverbad(struct mtd_info *mtd, loff_t ofs, int getchip)
{
        /* only called when module_param ignore_badblocks is set */
        return 0;
}

static void docg4_write_buf16(struct mtd_info *mtd, const uint8_t *buf, int len)
{
        int i;
        struct nand_chip *nand = mtd->priv;
        uint16_t *p = (uint16_t *)buf;
        len >>= 1;

        for (i = 0; i < len; i++)
                writew(p[i], nand->IO_ADDR_W);
}

static int write_page(struct mtd_info *mtd, struct nand_chip *nand,
                       const uint8_t *buf, int use_ecc)
{
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;
        uint8_t ecc_buf[8];

        writew(DOC_ECCCONF0_ECC_ENABLE |
               DOC_ECCCONF0_UNKNOWN |
               DOCG4_BCH_SIZE,
               docptr + DOC_ECCCONF0);
        write_nop(docptr);

        /* write the page data */
        docg4_write_buf16(mtd, buf, DOCG4_PAGE_SIZE);

        /* oob bytes 0 through 5 are written to I/O reg */
        docg4_write_buf16(mtd, nand->oob_poi, 6);

        /* oob byte 6 written to a separate reg */
        writew(nand->oob_poi[6], docptr + DOCG4_OOB_6_7);

        write_nop(docptr);
        write_nop(docptr);

        /* write hw-generated ecc bytes to oob */
        if (likely(use_ecc)) {
                /* oob byte 7 is hamming code */
                uint8_t hamming = readb(docptr + DOC_HAMMINGPARITY);
                hamming = readb(docptr + DOC_HAMMINGPARITY); /* 2nd read */
                writew(hamming, docptr + DOCG4_OOB_6_7);
                write_nop(docptr);

                /* read the 7 bch bytes from ecc regs */
                read_hw_ecc(docptr, ecc_buf);
                ecc_buf[7] = 0;         /* clear the "page written" flag */
        }

        /* write user-supplied bytes to oob */
        else {
                writew(nand->oob_poi[7], docptr + DOCG4_OOB_6_7);
                write_nop(docptr);
                memcpy(ecc_buf, &nand->oob_poi[8], 8);
        }

        docg4_write_buf16(mtd, ecc_buf, 8);
        write_nop(docptr);
        write_nop(docptr);
        writew(0, docptr + DOC_DATAEND);
        write_nop(docptr);

        return 0;
}

static int docg4_write_page_raw(struct mtd_info *mtd, struct nand_chip *nand,
                                 const uint8_t *buf, int oob_required)
{
        return write_page(mtd, nand, buf, 0);
}

static int docg4_write_page(struct mtd_info *mtd, struct nand_chip *nand,
                             const uint8_t *buf, int oob_required)
{
        return write_page(mtd, nand, buf, 1);
}

static int read_page(struct mtd_info *mtd, struct nand_chip *nand,
                     uint8_t *buf, int page, int use_ecc)
{
        struct docg4_priv *doc = nand->priv;
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;
        uint16_t status, edc_err, *buf16;

        writew(DOC_ECCCONF0_READ_MODE |
               DOC_ECCCONF0_ECC_ENABLE |
               DOC_ECCCONF0_UNKNOWN |
               DOCG4_BCH_SIZE,
               docptr + DOC_ECCCONF0);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);

        /* the 1st byte from the I/O reg is a status; the rest is page data */
        status = readw(docptr + DOC_IOSPACE_DATA);
        if (status & DOCG4_READ_ERROR) {
                printf("docg4_read_page: bad status: 0x%02x\n", status);
                writew(0, docptr + DOC_DATAEND);
                return -EIO;
        }

        docg4_read_buf(mtd, buf, DOCG4_PAGE_SIZE); /* read the page data */

        /* first 14 oob bytes read from I/O reg */
        docg4_read_buf(mtd, nand->oob_poi, 14);

        /* last 2 read from another reg */
        buf16 = (uint16_t *)(nand->oob_poi + 14);
        *buf16 = readw(docptr + DOCG4_MYSTERY_REG);

        /*
         * Diskonchips read oob immediately after a page read.  Mtd
         * infrastructure issues a separate command for reading oob after the
         * page is read.  So we save the oob bytes in a local buffer and just
         * copy it if the next command reads oob from the same page.
         */
        memcpy(doc->oob_buf, nand->oob_poi, 16);

        write_nop(docptr);

        if (likely(use_ecc)) {
                /* read the register that tells us if bitflip(s) detected  */
                edc_err = readw(docptr + DOC_ECCCONF1);
                edc_err = readw(docptr + DOC_ECCCONF1);

                /* If bitflips are reported, attempt to correct with ecc */
                if (edc_err & DOC_ECCCONF1_BCH_SYNDROM_ERR) {
                        int bits_corrected = correct_data(mtd, buf, page);
                        if (bits_corrected == -EBADMSG)
                                mtd->ecc_stats.failed++;
                        else
                                mtd->ecc_stats.corrected += bits_corrected;
                }
        }

        writew(0, docptr + DOC_DATAEND);
        return 0;
}


static int docg4_read_page_raw(struct mtd_info *mtd, struct nand_chip *nand,
                               uint8_t *buf, int oob_required, int page)
{
        return read_page(mtd, nand, buf, page, 0);
}

static int docg4_read_page(struct mtd_info *mtd, struct nand_chip *nand,
                           uint8_t *buf, int oob_required, int page)
{
        return read_page(mtd, nand, buf, page, 1);
}

static void docg4_erase_block(struct mtd_info *mtd, int page)
{
        struct nand_chip *nand = mtd->priv;
        struct docg4_priv *doc = nand->priv;
        void __iomem *docptr = CONFIG_SYS_NAND_BASE;
        uint16_t g4_page;

        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: page %04x\n", __func__, page);

        sequence_reset(docptr);

        writew(DOCG4_SEQ_BLOCKERASE, docptr + DOC_FLASHSEQUENCE);
        writew(DOC_CMD_PROG_BLOCK_ADDR, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);

        /* only 2 bytes of address are written to specify erase block */
        g4_page = (uint16_t)(page / 4);  /* to g4's 2k page addressing */
        writeb(g4_page & 0xff, docptr + DOC_FLASHADDRESS);
        g4_page >>= 8;
        writeb(g4_page & 0xff, docptr + DOC_FLASHADDRESS);
        write_nop(docptr);

        /* start the erasure */
        writew(DOC_CMD_ERASECYCLE2, docptr + DOC_FLASHCOMMAND);
        write_nop(docptr);
        write_nop(docptr);

        poll_status(docptr);
        writew(DOCG4_SEQ_FLUSH, docptr + DOC_FLASHSEQUENCE);
        writew(DOCG4_CMD_FLUSH, docptr + DOC_FLASHCOMMAND);
        writew(DOC_ECCCONF0_READ_MODE | 4, docptr + DOC_ECCCONF0);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);
        write_nop(docptr);

        read_progstatus(doc, docptr);

        writew(0, docptr + DOC_DATAEND);
        write_nop(docptr);
        poll_status(docptr);
        write_nop(docptr);
}

static int read_factory_bbt(struct mtd_info *mtd)
{
        /*
         * The device contains a read-only factory bad block table.  Read it and
         * update the memory-based bbt accordingly.
         */

        struct nand_chip *nand = mtd->priv;
        uint32_t g4_addr = mtd_to_docg4_address(DOCG4_FACTORY_BBT_PAGE, 0);
        uint8_t *buf;
        int i, block, status;

        buf = kzalloc(DOCG4_PAGE_SIZE, GFP_KERNEL);
        if (buf == NULL)
                return -ENOMEM;

        read_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
        status = docg4_read_page(mtd, nand, buf, 0, DOCG4_FACTORY_BBT_PAGE);
        if (status)
                goto exit;

        /*
         * If no memory-based bbt was created, exit.  This will happen if module
         * parameter ignore_badblocks is set.  Then why even call this function?
         * For an unknown reason, block erase always fails if it's the first
         * operation after device power-up.  The above read ensures it never is.
         * Ugly, I know.
         */
        if (nand->bbt == NULL)  /* no memory-based bbt */
                goto exit;

        /*
         * Parse factory bbt and update memory-based bbt.  Factory bbt format is
         * simple: one bit per block, block numbers increase left to right (msb
         * to lsb).  Bit clear means bad block.
         */
        for (i = block = 0; block < DOCG4_NUMBLOCKS; block += 8, i++) {
                int bitnum;
                uint8_t mask;
                for (bitnum = 0, mask = 0x80;
                     bitnum < 8; bitnum++, mask >>= 1) {
                        if (!(buf[i] & mask)) {
                                int badblock = block + bitnum;
                                nand->bbt[badblock / 4] |=
                                        0x03 << ((badblock % 4) * 2);
                                mtd->ecc_stats.badblocks++;
                                printf("factory-marked bad block: %d\n",
                                       badblock);
                        }
                }
        }
 exit:
        kfree(buf);
        return status;
}

static int docg4_block_markbad(struct mtd_info *mtd, loff_t ofs)
{
        /*
         * Mark a block as bad.  Bad blocks are marked in the oob area of the
         * first page of the block.  The default scan_bbt() in the nand
         * infrastructure code works fine for building the memory-based bbt
         * during initialization, as does the nand infrastructure function that
         * checks if a block is bad by reading the bbt.  This function replaces
         * the nand default because writes to oob-only are not supported.
         */

        int ret, i;
        uint8_t *buf;
        struct nand_chip *nand = mtd->priv;
        struct nand_bbt_descr *bbtd = nand->badblock_pattern;
        int block = (int)(ofs >> nand->bbt_erase_shift);
        int page = (int)(ofs >> nand->page_shift);
        uint32_t g4_addr = mtd_to_docg4_address(page, 0);

        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: %08llx\n", __func__, ofs);

        if (unlikely(ofs & (DOCG4_BLOCK_SIZE - 1)))
                printf("%s: ofs %llx not start of block!\n",
                       __func__, ofs);

        /* allocate blank buffer for page data */
        buf = kzalloc(DOCG4_PAGE_SIZE, GFP_KERNEL);
        if (buf == NULL)
                return -ENOMEM;

        /* update bbt in memory */
        nand->bbt[block / 4] |= 0x01 << ((block & 0x03) * 2);

        /* write bit-wise negation of pattern to oob buffer */
        memset(nand->oob_poi, 0xff, mtd->oobsize);
        for (i = 0; i < bbtd->len; i++)
                nand->oob_poi[bbtd->offs + i] = ~bbtd->pattern[i];

        /* write first page of block */
        write_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
        docg4_write_page(mtd, nand, buf, 1);
        ret = pageprog(mtd);
        if (!ret)
                mtd->ecc_stats.badblocks++;

        kfree(buf);

        return ret;
}

static uint8_t docg4_read_byte(struct mtd_info *mtd)
{
        struct nand_chip *nand = mtd->priv;
        struct docg4_priv *doc = nand->priv;

        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s\n", __func__);

        if (doc->last_command.command == NAND_CMD_STATUS) {
                int status;

                /*
                 * Previous nand command was status request, so nand
                 * infrastructure code expects to read the status here.  If an
                 * error occurred in a previous operation, report it.
                 */
                doc->last_command.command = 0;

                if (doc->status) {
                        status = doc->status;
                        doc->status = 0;
                }

                /* why is NAND_STATUS_WP inverse logic?? */
                else
                        status = NAND_STATUS_WP | NAND_STATUS_READY;

                return status;
        }

        printf("unexpectd call to read_byte()\n");

        return 0;
}

static int docg4_wait(struct mtd_info *mtd, struct nand_chip *nand)
{
        struct docg4_priv *doc = nand->priv;
        int status = NAND_STATUS_WP;       /* inverse logic?? */
        MTDDEBUG(MTD_DEBUG_LEVEL3, "%s...\n", __func__);

        /* report any previously unreported error */
        if (doc->status) {
                status |= doc->status;
                doc->status = 0;
                return status;
        }

        status |= poll_status(CONFIG_SYS_NAND_BASE);
        return status;
}

int docg4_nand_init(struct mtd_info *mtd, struct nand_chip *nand, int devnum)
{
        uint16_t id1, id2;
        struct docg4_priv *docg4;
        int retval;

        docg4 = kzalloc(sizeof(*docg4), GFP_KERNEL);
        if (!docg4)
                return -1;

        mtd->priv = nand;
        nand->priv = docg4;

        /* These must be initialized here because the docg4 is non-standard
         * and doesn't produce an id that the nand code can use to look up
         * these values (nand_scan_ident() not called).
         */
        mtd->size = DOCG4_CHIP_SIZE;
        mtd->name = "Msys_Diskonchip_G4";
        mtd->writesize = DOCG4_PAGE_SIZE;
        mtd->erasesize = DOCG4_BLOCK_SIZE;
        mtd->oobsize = DOCG4_OOB_SIZE;

        nand->IO_ADDR_R =
                (void __iomem *)CONFIG_SYS_NAND_BASE + DOC_IOSPACE_DATA;
        nand->IO_ADDR_W = nand->IO_ADDR_R;
        nand->chipsize = DOCG4_CHIP_SIZE;
        nand->chip_shift = DOCG4_CHIP_SHIFT;
        nand->bbt_erase_shift = DOCG4_ERASE_SHIFT;
        nand->phys_erase_shift = DOCG4_ERASE_SHIFT;
        nand->chip_delay = 20;
        nand->page_shift = DOCG4_PAGE_SHIFT;
        nand->pagemask = 0x3ffff;
        nand->badblockpos = NAND_LARGE_BADBLOCK_POS;
        nand->badblockbits = 8;
        nand->ecc.layout = &docg4_oobinfo;
        nand->ecc.mode = NAND_ECC_HW_SYNDROME;
        nand->ecc.size = DOCG4_PAGE_SIZE;
        nand->ecc.prepad = 8;
        nand->ecc.bytes = 8;
        nand->ecc.strength = DOCG4_T;
        nand->options = NAND_BUSWIDTH_16 | NAND_NO_SUBPAGE_WRITE;
        nand->controller = &nand->hwcontrol;

        /* methods */
        nand->cmdfunc = docg4_command;
        nand->waitfunc = docg4_wait;
        nand->select_chip = docg4_select_chip;
        nand->read_byte = docg4_read_byte;
        nand->block_markbad = docg4_block_markbad;
        nand->read_buf = docg4_read_buf;
        nand->write_buf = docg4_write_buf16;
        nand->scan_bbt = nand_default_bbt;
        nand->erase_cmd = docg4_erase_block;
        nand->ecc.read_page = docg4_read_page;
        nand->ecc.write_page = docg4_write_page;
        nand->ecc.read_page_raw = docg4_read_page_raw;
        nand->ecc.write_page_raw = docg4_write_page_raw;
        nand->ecc.read_oob = docg4_read_oob;
        nand->ecc.write_oob = docg4_write_oob;

        /*
         * The way the nand infrastructure code is written, a memory-based bbt
         * is not created if NAND_SKIP_BBTSCAN is set.  With no memory bbt,
         * nand->block_bad() is used.  So when ignoring bad blocks, we skip the
         * scan and define a dummy block_bad() which always returns 0.
         */
        if (ignore_badblocks) {
                nand->options |= NAND_SKIP_BBTSCAN;
                nand->block_bad = docg4_block_neverbad;
        }

        reset(CONFIG_SYS_NAND_BASE);

        /* check for presence of g4 chip by reading id registers */
        id1 = readw(CONFIG_SYS_NAND_BASE + DOC_CHIPID);
        id1 = readw(CONFIG_SYS_NAND_BASE + DOCG4_MYSTERY_REG);
        id2 = readw(CONFIG_SYS_NAND_BASE + DOC_CHIPID_INV);
        id2 = readw(CONFIG_SYS_NAND_BASE + DOCG4_MYSTERY_REG);
        if (id1 != DOCG4_IDREG1_VALUE || id2 != DOCG4_IDREG2_VALUE)
                return -1;

        /* initialize bch algorithm */
        docg4->bch = init_bch(DOCG4_M, DOCG4_T, DOCG4_PRIMITIVE_POLY);
        if (docg4->bch == NULL)
                return -1;

        retval = nand_scan_tail(mtd);
        if (retval)
                return -1;

        /*
         * Scan for bad blocks and create bbt here, then add the factory-marked
         * bad blocks to the bbt.
         */
        nand->scan_bbt(mtd);
        nand->options |= NAND_BBT_SCANNED;
        retval = read_factory_bbt(mtd);
        if (retval)
                return -1;

        retval = nand_register(devnum);
        if (retval)
                return -1;

        return 0;
}